Fuel Pressure problem

[dryden3]

I have an '86 SVO that runs fine with the octane switch set to "unleaded," but setting it to "premium" makes it lose power and the oxygen sensor goes flat lean only under full boost. I hooked up my fuel pressure gauge and saw that under hard accel, fuel pressure initially rose up to 45 psi (as best I could see on the gauge in the dark), then just before full boost, the gauge needle started flickering fast between 40 and 45 psi, the engine started losing power, and the higher the rpm climbed, the lower fuel pressure got, down to 30 psi. I replaced the fuel filter about 1000 mi ago. The fuel pump has always whined loudly since I got the car over a year ago. Jumpering the "switch thingie (by the brake booster) that sends more voltage to the fuel pump when you are 'in the throttle'" makes the fuel pump whine at a higher pitch, but doesn't change the fuel pressure problem. I'm thinking the fuel pump is at fault, but here are my questions (and I don't mean to sound stupid!):

-Do I need any special tools to get get my pump out of the tank?

-Has anyone ever run into a problem similar to mine that was resolved by replacing the fuel pump?

-Is there anything else I should check before replacing the pump?

-Should I buy an aftermarket pump? My only mods are a Crane .420" lift roller cam, and a Sacramento-Mustang 3" downpipe.

Thanks everyone, I much appreciate your help!
John

[SVOeric]

-Do I need any special tools to get get my pump out of the tank?

not really, to take the tank off -- Drain it first,
I spray some WD-40 on the seal where the filler tube goes into the tank to make it easy to come out.
then take the 2 bolts off
and drop the tank on the ground
remove the connection to the fuel pump
use a brass (or something that wont SPARK) punch to tap the ring loose
work the fuel pump out, it takes a twist to get it out --

-Has anyone ever run into a problem similar to mine that was resolved by replacing the fuel pump?

OH YEA!! -- this is actually a common problem, especially for a 16 year old car!

-Is there anything else I should check before replacing the pump?

only other thing to think about would be the fuel pressure regulator. To test the pump, connect your fuel pressure gauge on the connector before it gets to the fuel rail. This should give you a better reading of what the pump is putting out.

-Should I buy an aftermarket pump? My only mods are a Crane .420" lift roller cam, and a Sacramento-Mustang 3" downpipe.

FOR SURE!!
You never know what your next mod may be, and remving the fuel tank to do this again SUX.. not to mention there is only a small $$$ price difference.
I would recomend getting a 255, high pressure pump. My theory on this is -- yea, it is a bit overkill, but in 10 years when it starts to get tired, it will still put out as much as a 190 LPH pump

the high pressure part comes in because on a boosted engine, you should raise 1 psi fuel pressure per # boost, so running 20 psi boost, you are looking at 60 psi fuel pressure, and that is pushing it on the lower end pumps.

[dryden3]

Thank-you Thank-you

Wow, thanks SVOeric for such good reply! I will check out my fuel pressure regulator and I will look for a 1 psi rise in fuel pressure per # of boost.
-What is fuel pressure supposed to be at idle and at key on engine off?
-What would you suggest for a brand/model# of a 255 lph fuel pump and can you recommend a good place to buy it from?

Again, thanks a whole lot for your advice.

later, John

[svono50]

John,

Your fuel pressure should be ~32psi at idle with the vacuum line connected and around 40psi with the vacuum line disconnected. As for key on/engine off you should see 30-40psi.

I would suggest finding a Walbro pump. Most vendors sell the Walbro brand. Try Paul @ SVPU or Jim @ Motion Dynamics first. If you don't find it there I would try Auto Performance Engineering (http://www.autoperformanceengineering.com/). They kind of started the mail order pump business for the GN folks. That is where I purchased my 155lph pump several years ago (it was the largest one at the time).

Good luck with your project.

[SVOeric]

yea... what he said

[dryden3]

Thanks Ted,

I'm going to run the tank out of gas before I drop it down, and I'm going to order up a Walbro pump. I'll let you know how it all turns out later!

[SvoTy]

Originally posted by dryden3
Thanks Ted,

I'm going to run the tank out of gas before I drop it down, and I'm going to order up a Walbro pump. I'll let you know how it all turns out later!

The Walbro part number for the hi pressure hi volume 255 pump is #GSS340.